Recently, with good thermal stability and a direct transition type energy band structure, Group III-based nitrides, such as gallium nitride (GaN), aluminum nitride (AlN), and the like, have been spotlighted as materials for light sources in the visible range and the ultraviolet range. Particularly, blue and green light emitting diodes using indium gallium nitride (InGaN) are used in various fields including large full color flat panel displays, signal lamps, interior lighting, high density light sources, high resolution output systems, optical communication, and the like.